1. Field of the Invention
The present invention relates to an optical communication technique and, more particularly, to a wavelength correction method and apparatus, wavelength check method and apparatus, which are used to correct the center wavelength output from an optical element, e.g., an arrayed waveguide diffraction grating having a slab waveguide, to a target value, when light is input to the optical element, a wavelength-corrected arrayed waveguide diffraction grating, and an interleaver.
2. Description of the Prior Art
A demand has arisen for an increase in transmission capacity in an optical fiber communication system as well as an increase in the volume of data transmitted. For this reason, a great deal of attention has been paid to DWDM (Dense Waveguide Division Multiplexing), and greater importance has been attached to optical elements such as an optical waveguide filter serving as a multiplexing/demultiplexing device for dividing/combining wavelengths.
Optical wavelength filters take various forms. Among these filters, an arrayed waveguide diffraction grating has wavelength characteristics represented by a narrow band and high extinction ratio, and also has characteristics as a multi-input/multi-output filter device. Therefore, this device allows demultiplexing a multiplexed signal or reverse operation, and hence allows easy formation of a wavelength multiplexing/demultiplexing device. In addition, if an arrayed waveguide diffraction grating is formed by using a quartz waveguide, good coupling to an optical fiber is ensured, and low insertion loss operation with an insertion loss of about several dB (decibel) can be realized. Owing to these advantages, among optical wavelength filters, an arrayed waveguide diffraction grating has attracted a great deal of attention as an important device and has been vigorously studied worldwide.
FIG. 1 shows the overall arrangement of a conventional arrayed waveguide diffraction grating. An arrayed waveguide diffraction grating 11 is comprised of one or a plurality of input waveguides 12 formed on a substrate (not shown), a plurality of output waveguides 13, a channel waveguide array 14 having waveguides bent at different curvatures, an input-side slab waveguide 15 which connects the input waveguides 12 to the channel waveguide array 14, and an output-side slab waveguide 16 which connects the channel waveguide array 14 to the output waveguides 13. The traveling path of multiplexed signal light incident from the input waveguides 12 is expanded by the input-side slab waveguide 15. The respective light components are then incident on the channel waveguide array 14 in equiphase. These incident light components vary in intensity at the respective incident positions in the input-side slab waveguide 15; the intensities increase toward the center, exhibiting an almost Gaussian distribution.
Predetermined optical path length differences are set among the respective arrayed waveguides constituting the channel waveguide array 14 such that the optical path lengths sequentially increase or decrease. Therefore, light components guided along the respective waveguides reach the output-side slab waveguide 16 with phase differences at predetermined intervals. In practice, owing to wavelength dispersion, equiphase planes tilt depending on the wavelengths. As a result, light components are imaged (focused) at different positions on the interfaces between the output-side slab waveguide 16 and the output waveguides 13 depending on the wavelengths. Since the output waveguides 13 are arranged at the respective positions corresponding to the wavelengths, arbitrary wavelength components can be extracted from the output waveguides 13.
The center wavelength of the arrayed waveguide diffraction grating 11 is very sensitive to a change in the refractive index of a waveguide material. In some case, therefore, the center wavelength varies due to variations in a film formation process as a manufacturing process, and the design value cannot be obtained. If the center wavelength varies, a high optical loss occurs at the wavelength used.
According to Japanese Unexamined Patent Publication No. 9-49936, therefore, input/output waveguides for wavelength correction are provided in addition to general input/output waveguides formed from AWGs (arrayed waveguides). The input/output waveguides are changed in accordance with the correction amount of wavelength.
If an angle difference in a demultiplexing direction with respect to a wavelength difference xcex4xcex is represented by xcex4xcex8, a center wavelength xcexn can be corrected by the value given by equation (1) by changing the positions of the input waveguides 12 in the arrayed waveguide diffraction grating, i.e., a slab incident angle xcex8 in.
xcex4xcexin=(xcex4xcex/xcex4xcex8)xc2x7xcex8in xe2x80x83xe2x80x83(1) 
These input/output waveguides for wavelength correction are, however, discretely arranged, resulting in discrete wavelength correction amounts. This makes it impossible to correct the wavelength to an arbitrary wavelength. In order to obtain an arbitrary wavelength correction amount, the slab incident angle xcex8in must be set to an arbitrary value.
FIG. 2 shows the arrangement of an arrayed waveguide diffraction grating designed to solve such a problem. According to, for example, the technique disclosed in xe2x80x9cP. CPU. Clements et al., IEEE, Photon, Tech, lett, Vol. 7, No. 10, pp. 1040-1041, 1995xe2x80x9d, a substrate is cut at a slab incident portion 22 on the input side of an AWG (arrayed waveguide) wafer 21. An input fiber 24 clamped between glass members 23 is bonded (fixed) to the slab incident portion 22 reinforced by a glass member. At the time of this bonding operation, centering is directly performed to arbitrarily change the position of the input fiber 24 in accordance with a wavelength correction amount.
FIG. 3 shows how slab centering is performed by this proposed arrayed waveguide diffraction grating. An ASE (Amplified Spontaneous Emission) light source 31 is connected to the input side of an input waveguide 12. The ASE light source 31 has wide-band wavelength characteristics like a white light source. The light output from the ASE light source 31 is incident from the input waveguide 12 onto the input-side slab waveguide 15. The input-side slab waveguide 15 is cut in a direction almost perpendicular to the optical axis and separated into a first input-side waveguide component 15A and second input-side waveguide component 15B.
A spectrum analyzer 32 is connected to the output side of the output waveguide 13 to measure a wavelength. Prior to this measurement, the spectrum analyzer 32 is directly connected to the ASE light source 31 without the mediacy of the arrayed waveguide diffraction grating to measure the amounts of light output the light source at the respective wavelengths in advance. In this state, measurement is started on the light output from a port of output waveguides 13 to which the spectrum analyzer 32 is connected. Measurement is performed while the relative position of the first input-side waveguide component 15A and second input-side waveguide component 15B is moved little by little in the direction as indicated by an arrow 33 in FIG. 3. The measured values are compared with the measurement results obtained while the arrayed waveguide diffraction grating is not connected to the ASE light source 31, and the differences are taken into consideration. The respective output light amounts are discriminated as specific values for the respective wavelengths to obtain a center wavelength, thereby correcting a wavelength shift.
Since the spectrum analyzer 32 is relatively expensive, such measurement is repeated while different ports are connected one by one. Theoretically, if the wavelength is corrected at one port, correction is done in all the channels of the arrayed waveguide diffraction grating. In practice, however, even if the center wavelength is corrected in one channel, the center wavelengths in the remaining channels are not necessarily corrected at the same time owing to fluctuations and the like in a manufacturing process. For this reason, similar measurement is performed at all ports to obtain the relative position of the first input-side waveguide component 15A and second input-side waveguide component 15B at which the wavelength shift becomes minimum, thereby completing wavelength correction. In a case of an arrayed waveguide diffraction grating having 40 channels, similar measurement is repeated for 40 ports. It therefore takes much time to perform such accurate wavelength correction.
Such a conventional wavelength correction method or apparatus has the problem of insufficient wavelength correction precision. The spectrum analyzer 32 analyzes wavelengths by using a diffraction grating (not shown) to extract a wavelength within a specific range using a slit having a finite width, and measures the light amount at the corresponding portion. The set slit width therefore becomes the limit value of wavelength resolution. This is called resolving power. At the present time, the resolving power is about 10 pm (picometer) to 15 pm. Wavelength correction cannot be done with precision exceeding this resolving power.
The slit is driven by a driving system such as a motor. Mechanical errors such as the flexure of a gear inevitably occur in the driving system. As a result, a subtle difference is produced between a wavelength as a control target and an actually controlled wavelength. This difference originates from the linearity, reproducibility, or absolute precision of the characteristics of mechanical parts. The limit of the practical attainable precision of a wavelength correction apparatus is about 30 pm. Even if, therefore, attempts are made to suppress the precision of the center wavelength of an arrayed waveguide diffraction grating to 5 pm or less, it is difficult to realize it.
The problems posed in measurement using the wide-band ASE light source 31 have been described above. A tunable wavelength light source which changes its output wavelength can be used in place of such a wide-band light source. In this case, a power meter is used in place of the spectrum analyzer 32 to measure an output light amount while shifting an input wavelength. Therefore, the problem of low resolving power, which occurs when the spectrum analyzer 32 is used, can be solved. In addition, wavelength correction can be done with sufficient precision by changing the relative position of the first input-side waveguide component 15A and second input-side waveguide component 15B while changing the wavelength of the tunable wavelength light source with high precision.
When wavelength correction is to be performed by the latter method using the tunable wavelength light source, a light amount is measured by the power meter by using a predetermined wavelength while the first input-side waveguide component 15A and second input-side waveguide component 15B are set to a given relative position. Subsequently, the wavelength is shifted little by little, and light amount measurement is repeated at each wavelength. Unlike in the former method using a wide-band light source and spectrum analyzer, in the latter method, the operation of setting a new wavelength and measuring a light amount must be repeated finely in the entire range of measurement wavelengths. The shift amount of wavelength is kept observed. When the center wavelength coincides with the target wavelength at a given relative position, the correction is terminated.
Obviously, the above description is made on correcting operation for one channel. Even if the center wavelength is corrected in one channel, it does not necessarily indicate that optimal correction is made in the remaining channels, because there are errors in a manufacturing process. In the latter correction method using a tunable wavelength light source, therefore, similar correcting operation must be repeated for the remaining channels. Finally, the relative position of the first input-side waveguide component 15A and second input-side waveguide component 15B is determined. Although a center wavelength can be corrected with sufficient precision by the latter correction method, it takes a very long period of time to perform correction.
In general, the time required for correction corresponds to the value obtained by multiplying the sum of the time required for movement between slab waveguides and the time required for measurement of a spectrum by the number of times the slab waveguide is moved. Assume that an optical power meter is used. In this case, even if the net time required for each measurement is about 1 sec, the operation of moving the optical power meter to the next measurement position must be repeated by the number of times the slab waveguide is moved. In practice, therefore, the time required for measurement for one arrayed waveguide diffraction grating is 5 min or more.
The above description has been made on wavelength correction in an arrayed waveguide diffraction grating. However, similar problems arise in wavelength correction in other optical elements and a wavelength check to be done to check whether the wavelength of an optical element of a product at the time of shipment complies with a required specification.
The present invention has been made in consideration of the above situation in the prior art, and has as its object to provide a wavelength correction method and apparatus and a wavelength check method and apparatus, which can quickly and easily correct and check the wavelength of an optical element having a waveguide such as an arrayed waveguide diffraction grating, an arrayed waveguide diffraction grating which is to be corrected or has been corrected, and an interleaver.
In order to achieve the above object, according to the first aspect of the present invention, there is provided a wavelength correction method in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component so as to be parallel with the predetermined end face, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, comprising the first-wavelength-based measurement step of causing a light component having a first wavelength xcex1 shifted from a target center wavelength xcexg by a predetermined wavelength to be incident from the waveguide component placed on, an incident side, and at the same time, measuring a level of a light component output at each movement position while moving at least one of the two waveguide components in a direction crossing the optical axis, the second-wavelength-based measurement step of causing a light component having a second wavelength xcex2 symmetrical to the first wavelength xcex1 with respect to the center wavelength xcexg to be incident from the waveguide component placed on the incident side, and at the same time, measuring a level of a light component output via the two waveguide components at each movement position while moving at least one of the two waveguide components in the direction crossing the optical axis, the coincident position discrimination step of discriminating a relative movement position of the two waveguide components at which the level of the light component obtained in the first-wavelength-based measurement step coincides with the level of the light component obtained in the second-wavelength-based measurement step, and the final correction step of fixing a positional relationship between the two waveguide components in the direction crossing the optical axis to the relative movement position discriminated in the coincident position discrimination step in order to complete correction for the center wavelength xcexg.
According to the first aspect, in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component so as to be parallel with the predetermined end face, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, light having the first wavelength xcex1 shifted from the center wavelength xcexg as the correction target by the predetermined wavelength is incident on the waveguide component on the incident side. In this state, the level of output light is measured while the relative position of the two waveguide components is changed. Likewise, light having the second wavelength xcex2 on the opposite side of the wavelength xcexg as a middle point to the first wavelength xcex1 is output, and similar measurement is performed. In this case, the two waveguide components may be obtained by cutting one slab waveguide or a slab waveguide assembly to which a waveguide is connected into two waveguides, or may be manufactured separately and their end faces are placed to oppose each other. In addition, these end faces may be formed by separating one slab waveguide into two waveguides or separating a slab waveguide assembly to which a waveguide portion is connected into two waveguides at the end face of the waveguide portion as a boundary.
If a waveform having the wavelength xcexg as a peak has a symmetrical shape on the short wavelength side and long wavelength side with the wavelength xcexg as the center, the level measured at the first wavelength xcex1 should coincide with that measured at the second wavelength xcex2. In the coincident position discrimination step, a relative movement position is discriminated, at which the level of light obtained in the first-wavelength-based measurement step coincides with the level of light obtained in the second-wavelength-based measurement step, and the positional relationship between the two waveguide components in the direction crossing the optical axis is fixed to the discriminated relative movement position, thereby terminating correction for the center wavelength xcexg.
In order to achieve the above object, according to the second aspect of the present invention, there is provided a wavelength correction method in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component so as to be parallel with the predetermined end face, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, comprising the wavelength time-divisional measurement step of causing a light component having a first wavelength xcex1 shifted from a target center wavelength xcexg by a predetermined wavelength and a light component having a second wavelength xcex2 symmetrical to the first wavelength to be alternately and periodically incident from the wavelength component placed on an incident side, and at the same time, measuring levels of light components output via the two waveguide components at each movement position while moving at least one of the two waveguide components in a direction crossing the optical axis, the level comparison step of comparing the levels of the two light components output through the two waveguide components, which are measured in the wavelength time-divisional measurement step, based on the wavelengths xcex1 and xcex2, and the final correction step of fixing a positional relationship between the waveguide component placed on the incident side and the waveguide component placed on an exit side to a position where the levels of the two light components coincide with each other in the level comparison step in order to complete correction for the center wavelength xcexg.
According to the second aspect, in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component so as to be parallel with the predetermined end face, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, light components having the first and second wavelengths xcex1 and xcex2 are alternately and repeatedly output with the center wavelength xcexg as the correction target being a middle point, and an output level at each position in this relationship is measured. In this case, the two waveguide components may be obtained by cutting one slab waveguide or a slab waveguide assembly to which a waveguide is connected into two waveguides, or may be manufactured separately and their end faces are placed to oppose each other. In addition, these end faces may be formed by separating one slab waveguide into two waveguides or separating a slab waveguide assembly to which a waveguide portion is connected into two waveguides at the end face of the waveguide portion as a boundary.
If a waveform having the wavelength xcexg as a peak has a symmetrical shape on the short wavelength side and long wavelength side with the wavelength xcexg as the center, the level measured at the first wavelength xcex1 should coincide with that measured at the second wavelength xcex2. In the coincident position discrimination step, a relative movement position is discriminated, at which the level of light obtained in the first-wavelength-based measurement step coincides with the level of light obtained in the second-wavelength-based measurement step, and the positional relationship between the two waveguide components in the direction crossing the optical axis is fixed to the discriminated relative movement position, thereby terminating correction for the center wavelength xcexg.
According to the third aspect of the present invention, in the wavelength correction method according to the first or second aspect, the interval between the first and second wavelengths xcex1 and xcex2 is a full-width at half-maximum of a spectrum, and a middle point between the wavelengths coincides with the wavelength xcexg.
The first and second wavelengths xcex1 and xcex2 may have values other than those described above. However, if the interval between the two wavelengths is set to the full-width at half-maximum of the spectrum, correction can be made at a position conforming to the definition of a center wavelength.
According to the fourth aspect of the present invention, in the wavelength correction method according to the first aspect, another slab waveguide is connected to an output side of the slab waveguide via a channel waveguide array, and in the final correction step, measurement is done to obtain a relative positional relationship between the slab waveguide and the another slab waveguide connected to the output side of the slab waveguide on the basis of levels of light components output from the two slab waveguides, and the positional relationship between the two slab waveguides is fixed on the basis of the measurement result in order to terminate correction for the center wavelength xcexg.
According to the fourth aspect, therefore, the center wavelength xcexg can be accurately corrected by, for example, averaging the correction results obtained on the respective output waveguides arranged on the output side of the channel waveguide array.
In order to achieve the above object, according to the fifth aspect of the present invention, there is provided a wavelength correction apparatus in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component so as to be parallel with the predetermined end face, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, comprising first-wavelength-based measurement means for causing a light component having a first wavelength xcex1 shifted from a target center wavelength xcexg by a predetermined wavelength to be incident from the waveguide component placed on an incident side, and at the same time, measuring a level of a light component output at each movement position while moving at least one of the two waveguide components in a direction crossing the optical axis, second-wavelength-based measurement means for causing a light component having a second wavelength xcex2 symmetrical to the first wavelength xcex1 with respect to the center wavelength xcexg to be incident from the waveguide component placed on the incident side, and at the same time, measuring a level of a light component output via the two waveguide components at each movement position while moving at least one of the two waveguide components in the direction crossing the optical axis, coincident position discrimination means for discriminating a relative movement position of the two waveguide components at which the level of the light component obtained by the first-wavelength-based measurement means coincides with the level of the light component obtained by the second-wavelength-based measurement means, and final correction means for fixing a positional relationship between the two waveguide components in the direction crossing the optical axis to the relative movement position discriminated in the coincident position discrimination step in order to complete correction for the center wavelength xcexg.
According to the fifth aspect, in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component so as to be parallel with the predetermined end face, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, light having the first wavelength xcex1 shifted from the center wavelength xcexg as the correction target by the predetermined wavelength is incident on the waveguide component on the incident side. In this state, the level of output light is measured at each position while the relative position of the two waveguide components is changed. In addition, light having the second wavelength xcex2 on the opposite side of the wavelength xcexg as a middle point to the first wavelength xcex1 is output, and similar measurement is performed. In this case, the two waveguide components may be obtained by cutting one slab waveguide or a slab waveguide assembly to which a waveguide is connected into two waveguides, or may be manufactured separately and their end faces are placed to oppose each other. In addition, these end faces may be formed by separating one slab waveguide into two waveguides or separating a slab waveguide assembly to which a waveguide portion is connected into two waveguides at the end face of the waveguide portion as a boundary.
If a waveform having the wavelength xcexg as a peak has a symmetrical shape on the short wavelength side and long wavelength side with the wavelength xcexg as the center, the level measured at the first wavelength xcex1 should coincide with that measured at the second wavelength xcex2. In the coincident position discrimination step, a relative movement position is discriminated, at which the level of light obtained in the first-wavelength-based measurement step coincides with the level of light obtained in the second-wavelength-based measurement step, and the positional relationship between the two waveguide components in the direction crossing the optical axis is fixed to the discriminated relative movement position, thereby terminating correction for the center wavelength xcexg.
In order to achieve the above object, according to the sixth aspect of the present invention, there is provided a wavelength correction apparatus in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component so as to be parallel with the predetermined end face, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, comprising wavelength time-divisional measurement means for causing a light component having a first wavelength xcex1 shifted from a target center wavelength xcexg by a predetermined wavelength and a light component having a second wavelength xcex2 symmetrical to the first wavelength to be alternately and periodically incident from the wavelength component placed on an incident side, and at the same time, measuring levels of light components output via the two waveguide components at each movement position while moving at least one of the two waveguide components in a direction crossing the optical axis, level comparison, means for comparing the levels of the two light components output through the two waveguide components, which are measured by the wavelength time-divisional measurement means, based on the wavelengths xcex1 and xcex2, and final correction means for fixing a positional relationship between the waveguide component placed on the incident side and the waveguide component placed on an exit side to a position where the levels of the two light components coincide with each other by the level comparison means in order to complete correction for the center wavelength xcexg.
According to the sixth aspect, in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component so as to be parallel with the predetermined end face, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, light components having the first and second wavelengths xcex1 and xcex2 are alternately and repeatedly output with the center wavelength xcexg as the correction target being a middle point, and output levels at the respective positions of the two waveguide components are measured on the basis of this relationship. In this case, the two waveguide components may be obtained by cutting one slab waveguide or a slab waveguide assembly to which a waveguide is connected into two waveguides, or may be manufactured separately and their end faces are placed to oppose each other. In addition, these end faces may be formed by separating one slab waveguide into two waveguides or separating a slab waveguide assembly to which a waveguide portion is connected into two waveguides at the end face of the waveguide portion as a boundary.
If a waveform having the wavelength xcexg as a peak has a symmetrical shape on the short wavelength side and long wavelength side with the wavelength xcexg as the center, the level measured at the first wavelength xcex1 should coincide with that measured at the second wavelength xcex2. In the coincident position discrimination step, a relative movement position is discriminated, at which the level of light obtained in the first-wavelength-based measurement step coincides with the level of light obtained in the second-wavelength-based measurement step, and the positional relationship between the two waveguide components in the direction crossing the optical axis is fixed to the discriminated relative movement position, thereby terminating correction for the center wavelength xcexg.
According to the seventh aspect of the present invention, in the wavelength correction apparatus according to the fifth or sixth aspect, the interval between the first and second wavelengths xcex1 and xcex2 is a full-width at half-maximum of a spectrum, and a middle point between the wavelengths coincides with the wavelength xcexg.
In the seventh aspect, the first and second wavelengths xcex1 and xcex2 may have values other than those described above. However, if the interval between the two wavelengths is set to the full-width at half-maximum of the spectrum, correction can be made at a position conforming to the definition of a center wavelength.
According to the eighth aspect of the present invention, in the wavelength correction apparatus according to the fifth aspect, another slab waveguide is connected to an output side of the slab waveguide via a channel waveguide array, and in the final correction means, measurement is done to obtain a relative positional relationship between the slab waveguide and the another slab waveguide connected to the output side of the slab waveguide on the basis of levels of light components output from the two slab waveguides, and the positional relationship between the two slab waveguides is fixed on the basis of the measurement result to terminate correction for the center wavelength xcexg.
According to the eighth aspect, therefore, the center wavelength xcexg can be accurately corrected by, for example, averaging the correction results obtained on the respective output waveguides arranged on the output side of the channel waveguide array.
In order to achieve the above object, according to the ninth aspect of the present invention, there is provided a wavelength correction method comprising the first wavelength incidence time power detection step of, when a light component having a first wavelength xcex1 shifted from a specific wavelength by a predetermined wavelength is incident on a specific waveguide which can change a wavelength characteristic, detecting an intensity of light emerging from the specific waveguide, the second waveguide incidence time power detection step of when a light component having a second wavelength xcex2 symmetrical to the first wavelength xcex1 with respect to the specific wavelength is incident, detecting an intensity of light emerging from the specific waveguide, and the characteristic changing step of changing a characteristic of the specific waveguide such that the intensities of light detected in the first and second wavelength incidence time detection steps coincide with each other.
In the ninth aspect, it is assumed that the waveform having the specific wavelength as a peak has a symmetrical shape on the short wavelength side and long wavelength side with the specific wavelength as the center. The characteristics of a specific waveguide is changed such that the intensity of light emerging from this specific waveguide when light having the first wavelength xcex1 shifted from the specific wavelength by a predetermined wavelength is incident on the specific waveguide coincides with the intensity of light emerging from the specific waveguide when light having the second wavelength xcex2 symmetrical to the first wavelength xcex1 with respect to the specific wavelength as the center is incident. This makes it possible to properly correct the wavelength characteristics of the specific waveguide.
According to the 10th aspect of the present invention, in the wavelength correction method according to the ninth aspect, in the characteristic changing step, the characteristic is changed by heating the specific waveguide.
In the 10th aspect, the wavelength characteristics of the specific waveguide are changed by heating. For example, a resistive element is placed in a waveguide and energized to apply a heat pulse to the waveguide, thereby changing the characteristics.
According to the 11th aspect of the present invention, in the wavelength correction method according to the ninth aspect, in the characteristic changing step, the characteristic is changed by heating the specific waveguide.
In the 11th aspect, the wavelength characteristics of the specific waveguide are changed by irradiation of ultraviolet light.
In order to achieve the above object, according to the 12th aspect of the present invention, there is provided a wavelength correction apparatus comprising light incidence means for selectively causing light having a first wavelength xcex1 shifted from a specific wavelength by a predetermined wavelength and a light component having a wavelength xcex2 which is symmetrical to the first wavelength xcex1 with respect to the specific wavelength to be incident on a specific waveguide which can change a wavelength characteristic, first wavelength incidence time power detection means for, when the light component having the first wavelength xcex1 is made incident by the light incidence means, detecting an intensity of light emerging from the specific waveguide, second wavelength incidence time power detection means for, when the light component having the second wavelength xcex2 is made incident by the light incidence means, detecting an intensity of light emerging from the specific waveguide, and characteristic changing means for changing a characteristic of the specific waveguide such that the intensities of light detected by the first and second wavelength incidence time power detection means coincide with each other.
In the 12th aspect, it is assumed that the waveform having the specific wavelength as a peak has a symmetrical shape on the short wavelength side and long wavelength side with the specific wavelength as the center. The characteristics of a specific waveguide is changed such that the intensity of light emerging from this specific waveguide when light having the first wavelength xcex1 shifted from the specific wavelength by a predetermined wavelength is incident on the specific waveguide coincides with the intensity of light emerging from the specific waveguide when light having the second wavelength xcex2 symmetrical to the first wavelength xcex1 with respect to the specific wavelength as the center is incident. This makes it possible to properly correct the wavelength characteristics of the specific waveguide.
According to the 13th aspect of the present invention, in the wavelength correction apparatus according to the 12th aspect, the characteristic changing means changes the characteristic by heating the specific waveguide.
In the 13th aspect, the wavelength characteristics of the specific waveguide are changed by heating. For example, a resistive element is placed in a waveguide and energized to apply a heat pulse to the waveguide so as to change the characteristics.
According to the 14th aspect of the present invention, in the wavelength correction apparatus according to the 12th aspect, the characteristic changing means changes the characteristic by irradiating the specific waveguide with ultraviolet light.
In the 14th aspect, the wavelength characteristics of the specific waveguide are changed by irradiation of ultraviolet light.
In order to achieve the above object, according to the 15th aspect of the present invention, there is provided a wavelength check method comprising the first wavelength incidence time power detection step of, when light having a first wavelength xcex1 shifted from a specific wavelength by a predetermined wavelength is incident on a specific waveguide, detecting an intensity of light emerging from the specific waveguide, the second wavelength incidence time power detection step of, when light having a second wavelength xcex2 symmetrical to the first wavelength xcex1 with respect to the specific wavelength is incident on the specific waveguide, detecting an intensity of light emerging from the specific waveguide, the comparison step of comparing the intensities of light detected in the first and second wavelength incidence time power detection steps, and the discrimination step of discriminating on the basis of the comparison result in the comparison step whether the specific wavelength coincides with a peak of light intensity in the specific waveguide.
According to the 15th aspect, if the light output from a specific waveguide exhibits a peak at a specific wavelength, the power of light is attenuated when the wavelength is shifted from the specific wavelength either to the short wavelength side or to the long wavelength side. Light components having the first and second wavelengths xcex1 and xcex2 located on the two sides of the specific wavelength are incident on the specific waveguide, and the intensities of light components emerging therefrom are compared with each other. It is then discriminated whether, for example, the comparison result falls within an allowable range. This makes it possible to discriminate the quality of the waveguide.
In order to achieve the above object, according to the 16th aspect of the present invention, there is provided a wavelength check apparatus comprising light incidence means for selectively causing light having a first wavelength xcex1 shifted from a specific wavelength by a predetermined wavelength and light having a second wavelength xcex2 symmetrical to the first wavelength xcex1 with respect to the specific wavelength to be incident on a specific waveguide, first wavelength incidence time power detection means for, when the light component having the first wavelength xcex1 is made incident by the light incidence means, detecting an intensity of light emerging from the specific waveguide, second wavelength incidence time power detection means for, when the light component having the second wavelength xcex2 is made incident by the light incidence means, detecting an intensity of light emerging from the specific waveguide, comparison means for detecting the intensities of light detected by the first and second wavelength incidence time power detection means, and discrimination means for discriminating on the basis of the comparison result obtained by the comparison means whether the specific wavelength coincides with a peak of light intensity in the specific waveguide.
According to the 16th aspect, if the light output from a specific waveguide exhibits a peak at a specific wavelength, the power of light is attenuated when the wavelength is shifted from the specific wavelength either to the short wavelength side or to the long wavelength side. Light components having the first and second wavelengths xcex1 and xcex2 located on the two sides of the specific wavelength are incident on the specific waveguide, and the intensities of light components emerging therefrom are compared with each other. It is then discriminated whether, for example, the comparison result falls within an allowable range. This makes it possible to discriminate the quality of the waveguide.
In order to achieve the above object, according to the 17th aspect of the present invention, there is provided a wavelength correction method in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component as to be parallel with the predetermined end face such that the end faces are set at an initial position as a predetermined relative positional relationship in a direction crossing the optical axis, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, comprising the center wavelength measurement step of causing light having a predetermined wavelength width to be incident from a waveguide component placed on an incident side, and measuring a center wavelength xcex0 of light which has passed through a predetermined optical part connected to a waveguide component placed on an exit side, the first-wavelength-based measurement step of causing a light component having a first wavelength xcex1 shifted from a target center wavelength xcexg by a predetermined wavelength to be incident from the waveguide component placed on the incident side, and at the same time, measuring a level of a light component output at each movement position while moving at least one of the two waveguide components in a direction crossing the optical axis, the second-wavelength-based measurement step of causing a light component having a second wavelength xcex2 symmetrical to the first wavelength xcex1 with respect to the center wavelength xcexg to be incident from the waveguide component placed on the incident side, and at the same time, measuring a level of a light component output via the two waveguide components at each movement position while moving at least one of the two waveguide components in the direction crossing the optical axis, the coincident position discrimination step of discriminating a relative movement position of the two waveguide components at which the level of the light component obtained in the first-wavelength-based measurement step coincides with the level of the light component obtained in the second-wavelength-based measurement step, and the final correction step of fixing a positional relationship between the two waveguide components in the direction crossing the optical axis to the relative movement position discriminated in the coincident position discrimination step in order to complete correction for the center wavelength xcexg.
According to the 17th aspect, in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component as to be parallel with the predetermined end face such that the end faces are set at an initial position as a predetermined relative positional relationship in a direction crossing the optical axis, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, the center wavelength xcex0 of light output from this structure is measured. In this case, the two waveguide components may be obtained by cutting one slab waveguide or a slab waveguide assembly to which a waveguide is connected into two waveguides, or may be manufactured separately and their end faces are placed to oppose each other. In addition, these end faces may be formed by separating one slab waveguide into two waveguides or separating a slab waveguide assembly to which a waveguide portion is connected into two waveguides at the end face of the waveguide portion as a boundary.
According to the 17th aspect, since the center wavelength changes as the relative positional relationship between the two waveguide components changes, light having the first wavelength xcex1 shifted from the center wavelength xcexg as the correction target by a predetermined wavelength is incident on the waveguide component located on the incident side, and the level of light output at each position is measured while the relative position of the two waveguide components is changed in this state. Likewise, light having the second wavelength xcex2 on the opposite side of the wavelength xcexg as a middle point to the first wavelength xcex1 is output, and similar measurement is performed. If a waveform having the wavelength xcexg as a peak has a symmetrical shape on the short wavelength side and long wavelength side with the wavelength xcexg as the center, the level measured at the first wavelength xcex1 should coincide with that measured at the second wavelength xcex2. In the coincident position discrimination step, a relative movement position is discriminated, at which the level of light obtained in the first-wavelength-based measurement step coincides with the level of light obtained in the second-wavelength-based measurement step, and the positional relationship between the two waveguide components in the direction crossing the optical axis is fixed to the discriminated relative movement position, thereby terminating correction for the center wavelength xcexg.
In order to achieve the above object, according to the 18th aspect of the present invention, there is provided a wavelength correction method in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component as to be parallel with the predetermined end face such that the end faces are set at an initial position as a predetermined relative positional relationship in a direction crossing the optical axis, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, comprising the center wavelength measurement step of causing light having a predetermined wavelength width to be incident from a waveguide component placed on an incident side, and measuring a center wavelength xcex0 of light which has passed through a predetermined optical part connected to a waveguide component placed on an exit side, the temporary correction step of obtaining a difference between the center wavelength xcex0 obtained by measurement in the center wavelength measurement step and a target center wavelength xcexg, and temporarily moving at least one of the two waveguide components to a relative position where the center wavelength xcexg is to be obtained in a direction crossing the optical axis on the basis of the obtained difference, the first-wavelength-based measurement step of causing a light component having a first wavelength xcex1 shifted from the center wavelength xcexg by a predetermined wavelength to be incident from the waveguide component placed on the incident side, and at the same time, measuring a level of a light component output at each movement position while moving at least one of the two waveguide components, relative to the position to which the waveguide component has been moved in the temporary correction step, in a direction crossing the optical axis, the second-wavelength-based measurement step of causing a light component having a second wavelength xcex2 symmetrical to the first wavelength xcex1 with respect to the center wavelength xcexg to be incident from the waveguide component placed on the incident side, and at the same time, measuring a level of a light component output via the two waveguide components at each movement position while moving at least one of the two waveguide components, relative to the position to which the waveguide component has been moved in the temporary correction step, in the direction crossing the optical axis, the coincident position discrimination step of discriminating a relative movement position of the two waveguide components at which the level of the light component obtained in the first-wavelength-based measurement step coincides with the level of the light component obtained in the second-wavelength-based measurement step, and the final correction step of fixing a positional relationship between the two waveguide components in the direction crossing the optical axis to the relative movement position discriminated in the coincident position discrimination step in order to complete correction for the center wavelength xcexg.
According to the 18th aspect, in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component as to be parallel with the predetermined end face such that the end faces are set at an initial position as a predetermined relative positional relationship in a direction crossing the optical axis, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, the center wavelength xcex0 of light output from this structure is measured. In this case, the two waveguide components may be obtained by cutting one slab waveguide or a slab waveguide assembly to which a waveguide is connected into two waveguides, or may be manufactured separately and their end faces are placed to oppose each other. In addition, these end faces may be formed by separating one slab waveguide into two waveguides or separating a slab waveguide assembly to which a waveguide portion is connected into two waveguides at the end face of the waveguide portion as a boundary.
In the temporary correction step, the difference between the center wavelength xcex0 obtained by measurement in the center wavelength measurement step and the center wavelength xcexg as the correction target is obtained, and at least one of the two waveguide components is temporarily moved, in accordance with the obtained difference, in the direction crossing the optical axis up to the relative position where the center wavelength xcexg should be obtained. By this movement, the center wavelength is brought near to the wavelength xcexg, although it has a slight error, thereby terminating temporary correction as coarse correction. Thereafter, fine correction concerning position is executed. In this correction, with reference to the position determined by temporary correction, light having the first wavelength xcex1 shifted from the center wavelength xcexg as the correction target by a predetermined wavelength is incident on the waveguide component located on the incident side, and the level of output light is measured while the relative position of the two waveguide components is changed in this state. In addition, light having the second wavelength xcex2 on the opposite side of the wavelength xcexg as a middle point to the first wavelength xcex1 is output, and similar measurement is performed. If a waveform having the wavelength xcexg as a peak has a symmetrical shape on the short wavelength side and long wavelength side with the wavelength xcexg as the center, the level measured at the first wavelength xcex1 should coincide with that measured at the second wavelength xcex2. In the coincident position discrimination step, a relative movement position is discriminated, at which the level of light obtained in the first-wavelength-based measurement step coincides with the level of light obtained in the second-wavelength-based measurement step, and the positional relationship between the two waveguide components in the direction crossing the optical axis is fixed to the discriminated relative movement position, thereby terminating correction for the center wavelength xcexg.
In the 18th aspect, since a relative position near the wavelength xcexg is found out in the temporary correction step, the minimum range of position movement (scanning) in measurement based on the first and second wavelengths xcex1 and xcex2 can be discriminated accurately to some extent. This eliminates unnecessary scanning operation.
In order to achieve the above object, according to the 19th aspect of the present invention, there is provided a wavelength correction method in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component as to be parallel with the predetermined end face such that the end faces are set at an initial position as a predetermined relative positional relationship in a direction crossing the optical axis, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, comprising the center wavelength measurement step of causing light in a relatively wide band to be incident from a waveguide component placed on an incident side, and measuring a center wavelength xcex0 of light output via a channel waveguide array connected to an opposite side of a slab waveguide to the input-side waveguide, the temporary correction step of obtaining a difference between the center wavelength xcex0 obtained by measurement in the center wavelength measurement step and a target center wavelength xcexg, and temporarily moving at least one of the two waveguide components to a relative position where the center wavelength xcexg is to be obtained in a direction crossing the optical axis on the basis of the obtained difference, the first-wavelength-based measurement step of causing a light component having a first wavelength xcex1 shifted from the center wavelength xcexg by a predetermined wavelength to be incident from the waveguide component placed on the incident side, and at the same time, measuring a level of a light component output via the channel waveguide array at each movement position while moving at least one of the two waveguide components, relative to the position to which the waveguide component has been moved in the temporary correction step, in a direction crossing the optical axis, the second-wavelength-based measurement step of causing a light component having a second wavelength xcex2 symmetrical to the first wavelength xcex1 with respect to the center wavelength xcexg to be incident from the waveguide component placed on the incident side, and at the same time, measuring a level of a light component output via the channel waveguide array at each movement position while moving at least one of the two waveguide components, relative to the position to which the waveguide component has been moved in the temporary correction step, in the direction crossing the optical axis, the coincident position discrimination step of discriminating a relative movement position of the two waveguide components at which the level of the light component obtained in the first-wavelength-based measurement step coincides with the level of the light component obtained in the second-wavelength-based measurement step, and the final correction step of fixing a positional relationship between the two waveguide components in the direction crossing the optical axis to the relative movement position discriminated in the coincident position discrimination step in order to complete correction for the center wavelength xcexg.
According to the 19th aspect, in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component as to be parallel with the predetermined end face such that the end faces are set at an initial position as a predetermined relative positional relationship in a direction crossing the optical axis, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, the center wavelength xcex0 of light output from this structure is measured. In this case, the two waveguide components may be obtained by cutting one slab waveguide or a slab waveguide assembly to which a waveguide is connected into two waveguides, or may be manufactured separately and their end faces are placed to oppose each other. In addition, these end faces may be formed by separating one slab waveguide into two waveguides or separating a slab waveguide assembly to which a waveguide portion is connected into two waveguides at the end face of the waveguide portion as a boundary.
In the temporary correction step, the difference between the center wavelength xcex0 obtained by measurement in the center wavelength measurement step and the center wavelength xcexg as the correction target is obtained, and at least one of the two waveguide components is temporarily moved, in accordance with the obtained difference, in the direction crossing the optical axis up to the relative position where the center wavelength xcexg should be obtained. By this movement, the center wavelength is brought near to the wavelength xcexg, although it has a slight error, thereby terminating temporary correction as coarse correction. Thereafter, fine correction concerning position is executed. In this correction, with reference to the position determined by temporary correction, light having the first wavelength xcex1 shifted from the center wavelength xcexg as the correction target by a predetermined wavelength is incident on the waveguide component located on the incident side, and the level of light output via the channel waveguide array is measured while the relative position of the two waveguide components is changed in this state. In addition, light having the second wavelength xcex2 on the opposite side of the wavelength xcexg as a middle point to the first wavelength xcex1 is output, and similar measurement is performed. If a waveform having the wavelength xcexg as a peak has a symmetrical shape on the short wavelength side and long wavelength side with the wavelength xcexg as the center, the level measured at the first wavelength xcex1 should coincide with that measured at the second wavelength xcex2. In the coincident position discrimination step, a relative movement position is discriminated, at which the level of light obtained in the first-wavelength-based measurement step coincides with the level of light obtained in the second-wavelength-based measurement step, and the positional relationship between the two waveguide components in the direction crossing the optical axis is fixed to the discriminated relative movement position, thereby terminating correction for the center wavelength xcexg.
In the 19th aspect, since a relative position near the wavelength xcexg is found out in the temporary correction step, the minimum range of position movement (scanning) in measurement based on the first and second wavelengths xcex1 and xcex2 can be discriminated accurately to some extent. This eliminates unnecessary scanning operation. In addition, the slab waveguide is implemented as an arrayed waveguide diffraction grating or the like connected to a channel waveguide array as an optical part.
In order to achieve the above object, according to the 20th aspect of the present invention, there is provided a wavelength correction method in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component as to be parallel with the predetermined end face such that the end faces are set at an initial position as a predetermined relative positional relationship in a direction crossing the optical axis, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, comprising the center wavelength measurement step of causing light having a predetermined wavelength width to be incident from a waveguide component placed on an incident side, and measuring a center wavelength xcex0 of light which has passed through a predetermined optical part connected to a waveguide component placed on an exit side, the wavelength time-divisional measurement step of causing a light component having a first wavelength xcex1 and a light component having a second wavelength xcex2 which are symmetrical with respect to a target center wavelength xcexg to be alternately and periodically incident from the wavelength component placed on an incident side, and at the same time, measuring levels of light components output via the two waveguide components at each movement position while moving at least one of the two waveguide components in a direction crossing the optical axis, the level comparison step of comparing the levels of the two light components output through the optical part, which are measured in the wavelength time-divisional measurement step, based on the wavelengths xcex1 and xcex2, and the final correction step of fixing a positional relationship between the waveguide component placed on the incident side and the waveguide component placed on an exit side to a position where the levels of the two light components coincide with each other in the level comparison step in order to complete correction for the center wavelength xcexg.
According to the 20th aspect, in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component as to be parallel with the predetermined end face such that the end faces are set at an initial position as a predetermined relative positional relationship in a direction crossing the optical axis, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, the center wavelength xcex0 of light output from this structure is measured. In this case, the two waveguide components may be obtained by cutting one slab waveguide or a slab waveguide assembly to which a waveguide is connected into two waveguides, or may be manufactured separately and their end faces are placed to oppose each other. In addition, these end faces may be formed by separating one slab waveguide into two waveguides or separating a slab waveguide assembly to which a waveguide portion is connected into two waveguides at the end face of the waveguide portion as a boundary.
In the 20th aspect, since the center wavelength changes as the relative positional relationship between the two waveguide components changes, light components having the first and second wavelengths xcex1 and xcex2 are alternately and repeatedly output with the center wavelength xcexg as the correction target being a middle point, and an output level at each position in this relationship is measured. If a waveform having the wavelength xcexg as a peak has a symmetrical shape on the short wavelength side and long wavelength side with the wavelength xcexg as the center, the level measured at the first wavelength xcex1 should coincide with that measured at the second wavelength xcex2. In the coincident position discrimination step, a relative movement position is discriminated, at which the level of light obtained in the first-wavelength-based measurement step coincides with the level of light obtained in the second-wavelength-based measurement step, and the positional relationship between the two waveguide components in the direction crossing the optical axis is fixed to the discriminated relative movement position, thereby terminating correction for the center wavelength xcexg.
According to the 21st aspect of the present invention, in the wavelength correction method according to any one of the 17th to 20th aspects, the interval between the first and second wavelengths xcex1 and xcex2 is a full-width at half-maximum of a spectrum, and a middle point between the wavelengths coincides with the wavelength xcexg.
The first and second wavelengths xcex1 and xcex2 may have values other than those described above. However, if the interval between the two wavelengths is set to the full-width at half-maximum of the spectrum, correction can be made at a position conforming to the definition of a center wavelength.
According to the 22nd aspect of the present invention, in the wavelength correction method according to the 19th aspect, a plurality of output waveguides are connected to an output side of the channel waveguide array via another slab waveguide, and in the final correction step, measurement is done to obtain a relative positional relationship between the slab waveguide and the another slab waveguide connected to the output side of the slab waveguide on the basis of levels of light components output from the two slab waveguides, and the positional relationship between the two slab waveguides is fixed on the basis of the measurement result in order to terminate correction for the center wavelength xcexg.
According to the 22nd aspect, therefore, the center wavelength xcexg can be accurately corrected by, for example, averaging the correction results obtained on the respective output waveguides arranged on the output side of the channel waveguide array.
In order to achieve the above object, according to the 23rd aspect of the present invention, there is provided a wavelength correction apparatus in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component as to be parallel with the predetermined end face such that the end faces are set at an initial position as a predetermined relative positional relationship in a direction crossing the optical axis, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, comprising center wavelength measurement means for causing light having a predetermined wavelength width to be incident from a waveguide component placed on an incident side, and measuring a center wavelength xcex0 of light which has passed through a predetermined optical part connected to a waveguide component placed on an exit side, first-wavelength-based measurement means for causing a light component having a first wavelength xcex1 shifted from a target center wavelength xcexg by a predetermined wavelength to be incident from the waveguide component placed on the incident side, and at the same time, measuring a level of a light component output at each movement position while moving at least one of the two waveguide components in a direction crossing the optical axis, second-wavelength-based measurement means for causing a light component having a second wavelength xcex2 symmetrical to the first wavelength xcex1 with respect to the center wavelength xcexg to be incident from the waveguide component placed on the incident side, and at the same time, measuring a level of a light component output via the two waveguide components at each movement position while moving at least one of the two waveguide components in the direction crossing the optical axis, coincident position discrimination means for discriminating a relative movement position of the two waveguide components at which the level of the light component obtained by the first-wavelength-based measurement means coincides with the level of the light component obtained by the second-wavelength-based measurement means, and final correction means for fixing a positional relationship between the two waveguide components in the direction crossing the optical axis to the relative movement position discriminated by the coincident position discrimination means in order to complete correction for the center wavelength xcexg.
According to the 23rd aspect, in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component as to be parallel with the predetermined end face such that the end faces are set at an initial position as a predetermined relative positional relationship in a direction crossing the optical axis, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, the center wavelength xcex0 of light output from this structure is measured. In this case, the two waveguide components may be obtained by cutting one slab waveguide or a slab waveguide assembly to which a waveguide is connected into two waveguides, or may be manufactured separately and their end faces are placed to oppose each other. In addition, these end faces may be formed by separating one slab waveguide into two waveguides or separating a slab waveguide assembly to which a waveguide portion is connected into two waveguides at the end face of the waveguide portion as a boundary.
According to the 23rd aspect, since the center wavelength changes as the relative positional relationship between the two waveguide components changes, light having the first wavelength xcex1 shifted from the center wavelength xcexg as the correction target by a predetermined wavelength is incident on the waveguide component located on the incident side, and the level of light output at each position is measured while the relative position of the two waveguide components is changed in this state. Likewise, light having the second wavelength xcex2 on the opposite side of the wavelength xcexg as a middle point to the first wavelength xcex1 is output, and similar measurement is performed. If a waveform having the wavelength xcexg as a peak has a symmetrical shape on the short wavelength side and long wavelength side with the wavelength xcexg as the center, the level measured at the first wavelength xcex1 should coincide with that measured at the second wavelength xcex2. The coincident position discrimination means discriminates a relative movement position at which the level of light obtained by the first-wavelength-based measurement means coincides with the level of light obtained by the second-wavelength-based measurement means, and the positional relationship between the two waveguide components in the direction crossing the optical axis is fixed to the discriminated relative movement position, thereby terminating correction for the center wavelength xcexg.
In order to achieve the above object, according to the 24th aspect of the present invention, there is provided a wavelength correction apparatus in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component as to be parallel with the predetermined end face such that the end faces are set at an initial position as a predetermined relative positional relationship in a direction crossing the optical axis, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, comprising center wavelength measurement means for causing light having a predetermined wavelength width to be incident from a waveguide component placed on an incident side, and measuring a center wavelength xcex0 of light which has passed through a predetermined optical part connected to a waveguide component placed on an exit side, temporary correction means for obtaining a difference between the center wavelength xcex0 obtained by measurement by the center wavelength measurement means and a target center wavelength xcexg, and temporarily moving at least one of the two waveguide components to a relative position where the center wavelength xcexg is to be obtained in a direction crossing the optical axis on the basis of the obtained difference, first-wavelength-based measurement means for causing a light component having a first wavelength xcex1 shifted from the center wavelength xcexg by a predetermined wavelength to be incident from the waveguide component placed on the incident side, and at the same time, measuring a level of a light component output at each movement position while moving at least one of the two waveguide components, relative to the position to which the waveguide component has been moved by the temporary correction means, in a direction crossing the optical axis, second-wavelength-based measurement means for causing a light component having a second wavelength xcex2 symmetrical to the first wavelength xcex1 with respect to the center wavelength xcexg to be incident from the waveguide component placed on the incident side, and at the same time, measuring a level of a light component output via the two waveguide components at each movement position while moving at least one of the two waveguide components, relative to the position to which the waveguide component has been moved by the temporary correction means, in the direction crossing the optical axis, coincident position discrimination means for discriminating a relative movement position of the two waveguide components at which the level of the light component obtained by the first-wavelength-based measurement means coincides with the level of the light component obtained by the second-wavelength-based measurement means, and final correction means for fixing a positional relationship between the two waveguide components in the direction crossing the optical axis to the relative movement position discriminated by the coincident position discrimination means in order to complete correction for the center wavelength xcexg.
According to the 24th aspect, in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component as to be parallel with the predetermined end face such that the end faces are set at an initial position as a predetermined relative positional relationship in a direction crossing the optical axis, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, the center wavelength xcex0 of light output from this structure is measured. In this case, the two waveguide components may be obtained by cutting one slab waveguide or a slab waveguide assembly to which a waveguide is connected into two waveguides, or may be manufactured separately and their end faces are placed to oppose each other. In addition, these end faces may be formed by separating one slab waveguide into two waveguides or separating a slab waveguide assembly to which a waveguide portion is connected into two waveguides at the end face of the waveguide portion as a boundary.
The temporary correction means obtains the difference between the center wavelength xcex0 obtained by measurement in the center wavelength measurement step and the center wavelength xcexg as the correction target, and at least one of the two waveguide components is temporarily moved, in accordance with the obtained difference, in the direction crossing the optical axis up to the relative position where the center wavelength xcexg should be obtained. By this movement, the center wavelength is brought near to the wavelength xcexg, although it has a slight error, thereby terminating temporary correction as coarse correction. Thereafter, fine correction concerning position is executed. In this correction, with reference to the position determined by temporary correction, light having the first wavelength xcex1 shifted from the center wavelength xcexg as the correction target by a predetermined wavelength is incident on the waveguide component located on the incident side, and the level of output light is measured while the relative position of the two waveguide components is changed in this state. In addition, light having the second wavelength xcex2 on the opposite side of the wavelength xcexg as a middle point to the first wavelength xcex1 is output, and similar measurement is performed. If a waveform having the wavelength xcexg as a peak has a symmetrical shape on the short wavelength side and long wavelength side with the wavelength xcexg as the center, the level measured at the first wavelength xcex1 should coincide with that measured at the second wavelength xcex2. The coincident position discrimination means discriminates a relative movement position at which the level of light obtained by the first-wavelength-based measurement means coincides with the level of light obtained by the second-wavelength-based measurement means, and the positional relationship between the two waveguide components in the direction crossing the optical axis is fixed to the discriminated relative movement position, thereby terminating correction for the center wavelength xcexg.
In the 24th aspect, since a relative position near the wavelength xcexg is found out by the temporary correction means, the minimum range of position movement (scanning) in measurement based on the first and second wavelengths xcex1 and xcex2 can be discriminated accurately to some extent. This eliminates unnecessary scanning operation.
In order to achieve the above object, according to the 25th aspect of the present invention, there is provided a wavelength correction apparatus in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component as to be parallel with the predetermined end face such that the end faces are set at an initial position as a predetermined relative positional relationship in a direction crossing the optical axis, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, comprising center wavelength measurement means for causing light in a relatively wide band to be incident from a waveguide component placed on an incident side, and measuring a center wavelength xcex0 of light output via a channel waveguide array connected to an opposite side of a slab waveguide to the input-side waveguide, temporary correction means for obtaining a difference between the center wavelength xcex0 obtained by measurement by the center wavelength measurement means and a target center wavelength xcexg, and temporarily moving at least one of the two waveguide components to a relative position where the center wavelength xcexg is to be obtained in a direction crossing the optical axis on the basis of the obtained difference, first-wavelength-based measurement means for causing a light component having a first wavelength xcex1 shifted from the center wavelength xcexg by a predetermined wavelength to be incident from the waveguide component placed on the incident side, and at the same time, measuring a level of a light component output via the channel waveguide array at each movement position while moving at least one of the two waveguide components, relative to the position to which the waveguide component has been moved by the temporary correction means, in a direction crossing the optical axis, second-wavelength-based measurement means for causing a light component having a second wavelength xcex2 symmetrical to the first wavelength xcex1 with respect to the center wavelength xcexg to be incident from the waveguide component placed on the incident side, and at the same time, measuring a level of a light component output via the channel waveguide array at each movement position while moving at least one of the two waveguide components, relative to the position to which the waveguide component has been moved by the temporary correction means, in the direction crossing the optical axis, coincident position discrimination means for discriminating a relative movement position of the two waveguide components at which the level of the light component obtained by the first-wavelength-based measurement means coincides with the level of the light component obtained by the second-wavelength-based measurement means, and final correction means for fixing a positional relationship between the two waveguide components in the direction crossing the optical axis to the relative movement position discriminated by the coincident position discrimination means in order to complete correction for the center wavelength xcexg.
According to the 25th aspect, in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component as to be parallel with the predetermined end face such that the end faces are set at an initial position as a predetermined relative positional relationship in a direction crossing the optical axis, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, the center wavelength xcex0 of light output from this structure is measured. In this case, the two waveguide components may be obtained by cutting one slab waveguide or a slab waveguide assembly to which a waveguide is connected into two waveguides, or may be manufactured separately and their end faces are placed to oppose each other. In addition, these end faces may be formed by separating one slab waveguide into two waveguides or separating a slab waveguide assembly to which a waveguide portion is connected into two waveguides at the end face of the waveguide portion as a boundary.
The temporary correction step obtains the difference between the center wavelength xcex0 obtained by measurement done by the center wavelength measurement means and the center wavelength xcexg as the correction target is obtained, and at least one of the two waveguide components is temporarily moved, in accordance with the obtained difference, in the direction crossing the optical axis up to the relative position where the center wavelength xcexg should be obtained. By this movement, the center wavelength is brought near to the wavelength xcexg, although it has a slight error, thereby terminating temporary correction as coarse correction. Thereafter, fine correction concerning position is executed. In this correction, with reference to the position determined by temporary correction, light having the first wavelength xcex1 shifted from the center wavelength xcexg as the correction target by a predetermined wavelength is incident on the waveguide component located on the incident side, and the level of light output via the channel waveguide array is measured while the relative position of the two waveguide components is changed in this state. In addition, light having the second wavelength xcex2 on the opposite side of the wavelength xcexg as a middle point to the first wavelength xcex1 is output, and similar measurement is performed. If a waveform having the wavelength xcexg as a peak has a symmetrical shape on the short wavelength side and long wavelength side with the wavelength xcexg as the center, the level measured at the first wavelength xcex1 should coincide with that measured at the second wavelength xcex2. The coincident position discrimination means discriminates a relative movement position at which the level of light obtained by the first-wavelength-based measurement means coincides with the level of light obtained by the second-wavelength-based measurement means, and the positional relationship between the two waveguide components in the direction crossing the optical axis is fixed to the discriminated relative movement position, thereby terminating correction for the center wavelength xcexg.
In the 25th aspect, since a relative position near the wavelength xcexg is found out by the temporary correction means, the minimum range of position movement (scanning) in measuring based on the first and second wavelengths xcex1 and xcex2 can be discriminated accurately to some extent. This eliminates unnecessary scanning operation. In addition, the slab waveguide is implemented as an arrayed waveguide diffraction grating or the like connected to a channel waveguide array as an optical part.
In order to achieve the above object, according to the 26th aspect of the present invention, there is provided a wavelength correction apparatus in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component as to be parallel with the predetermined end face such that the end faces are set at an initial position as a predetermined relative positional relationship in a direction crossing the optical axis, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, comprising center wavelength measurement means for causing light having a predetermined wavelength width to be incident from a waveguide component placed on an incident side, and measuring a center wavelength xcex0 of light which has passed through a predetermined optical part connected to a waveguide component placed on an exit side, wavelength time-divisional measurement means for causing a light component having a first wavelength xcex1 and a light component having a second wavelength xcex2 which are symmetrical with respect to a target center wavelength xcexg to be alternately and periodically incident from the wavelength component placed on an incident side, and at the same time, measuring levels of light components output via the two waveguide components at each movement position while moving at least one of the two waveguide components in a direction crossing the optical axis, level comparison means for comparing the levels of the two light components output through the optical part, which are measured by the wavelength time-divisional measurement means, based on the wavelengths xcex1 and xcex2, and final correction means for fixing a positional relationship between the waveguide component placed on the incident side and the waveguide component placed on an exit side to a position where the levels of the two light components coincide with each other by the level comparison means in order to complete correction for the center wavelength xcexg.
According to the 26th aspect, in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component as to be parallel with the predetermined end face such that the end faces are set at an initial position as a predetermined relative positional relationship in a direction crossing the optical axis, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, the center wavelength xcex0 of light output from this structure is measured. In this case, the two waveguide components may be obtained by cutting one slab waveguide or a slab waveguide assembly to which a waveguide is connected into two waveguides, or may be manufactured separately and their end faces are placed to oppose each other. In addition, these end faces may be formed by separating one slab waveguide into two waveguides or separating a slab waveguide assembly to which a waveguide portion is connected into two waveguides at the end face of the waveguide portion as a boundary.
In the 26th aspect, since the center wavelength changes as the relative positional relationship between the two waveguide components changes, light components having the first and second wavelengths xcex1 and xcex2 are alternately and repeatedly output with the center wavelength xcexg as the correction target being a middle point, and an output level at each position in this relationship is measured. If a waveform having the wavelength xcexg as a peak has a symmetrical shape on the short wavelength side and long wavelength side with the wavelength xcexg as the center, the level measured at the first wavelength xcex1 should coincide with that measured at the second wavelength xcex2. The coincident position discrimination means discriminates a relative movement position at which the level of light obtained by the first-wavelength-based measurement means coincides with the level of light obtained by the second-wavelength-based measurement means, and the positional relationship between the two waveguide components in the direction crossing the optical axis is fixed to the discriminated relative movement position, thereby terminating correction for the center wavelength xcexg.
According to the 27th aspect of the present invention, in the wavelength correction apparatus according to any one of the 23rd to 26th aspects, the interval between the first and second wavelengths xcex1 and xcex2 is a full-width at half-maximum of a spectrum, and a middle point between the wavelengths coincides with the wavelength xcexg.
In the 27th aspect, the first and second wavelengths xcex1 and xcex2 may have values other than those described above. However, if the interval between the two wavelengths is set to the full-width at half-maximum of the spectrum, correction can be made at a position conforming to the definition of a center wavelength.
According to the 28th aspect of the present invention, in the wavelength correction apparatus according to the 25th aspect, a plurality of output waveguides are connected to the output side of the channel waveguide array via another slab waveguide, and the final correction means performs similar measurement to obtain the positional relationship with respect to light components respectively output from the plurality of output waveguides and fixes the positional relationship on the basis of the measurement result in order to terminate correction for the center wavelength xcexg.
According to the 28th aspect, therefore, the center wavelength xcexg can be accurately corrected by, for example, averaging the correction results obtained on the respective output waveguides arranged on the output side of the channel waveguide array.
In order to achieve the above object, according to the 29th aspect of the present invention, there is provided an arrayed waveguide diffraction grating in a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component as to be parallel with the predetermined end face, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, wherein at the time of first measurement, when light having a first wavelength xcex1 shifted from a target center wavelength xcexg by a predetermined wavelength is incident on a waveguide component placed on an incident side, a level of light output at each movement position is measured while at least one the two waveguide components is moved in a direction crossing the optical axis, at the time of second measurement, when light having a second wavelength xcex2 symmetrical to the first wavelength xcex1 with respect to the center wavelength xcexg is incident from the waveguide component placed on the incident side, a level of light output via the two waveguide components is measured at each movement position while at least one of the two waveguide components is moved in a direction crossing the optical axis, and a positional relationship between the two waveguide components in the direction crossing the optical axis is so fixed as to set a relative movement position where the level of light obtained at the time of first measurement coincides with the level of light obtained at the time of second measurement in order to perform correction for the center wavelength xcexg.
In a slab waveguide formed as one waveguide as a whole by combining two waveguide components with a predetermined end face which is so formed on one waveguide component as to cross an optical axis being placed to oppose an end face which is so formed on the other waveguide component so as to be parallel with the predetermined end face, or a slab waveguide assembly formed by connecting another waveguide to the slab waveguide, the first and second measurements are performed by using the arrayed waveguide diffraction grating according to the 29th aspect, and the positional relationship between the two waveguide components in the direction crossing the optical axis is fixed to the relative movement position where the levels of light components obtained by these measurements coincide with each other, thereby correcting the center wavelength xcexg.
In this case, the two waveguide components may be obtained by cutting one slab waveguide or a slab waveguide assembly to which a waveguide is connected into two waveguides, or may be manufactured separately and their end faces are placed to oppose each other. In addition, these end faces may be formed by separating one slab waveguide into two waveguides or separating a slab waveguide assembly to which a waveguide portion is connected into two waveguides at the end face of the waveguide portion as a boundary.
According to the 30th aspect of the present invention, there is provided an arrayed waveguide diffraction grating according to the 29th aspect, wherein the slab waveguide and another slab waveguide are connected via a channel waveguide array.
According to the 30th aspect, the arrangement obtained by connecting the two slab waveguides to the channel waveguide array is also implemented by an arrayed waveguide diffraction grating.
In order to achieve the above object, according to the 31st aspect of the present invention, there is provided an interleaver comprising an input waveguide, two optical waveguides which are connected to one end of the input waveguide and demultiplex input wavelength multiplexed light into light components of odd-numbered wavelengths and light components of even-numbered wavelengths, and characteristic correction means for changing a characteristic of the optical waveguide such that a measurement result on an intensity of light emerging from the optical waveguide, which is obtained when light having a first wavelength xcex1 shifted from a specific wavelength by a predetermined wavelength is incident on at least one of the optical waveguides, coincides with a measurement result on an intensity of light emerging from the optical waveguide, which is obtained when light having a second wavelength xcex2 symmetrical to the first wavelength xcex1 with respect to the specific wavelength is incident.
According to the 31st aspect, the interleaver includes the characteristic correction means for correcting characteristics by measurement using the two wavelengths xcex1 and xcex2 having a predetermined relationship with at least one of the two optical waveguides.
According to the 32nd aspect of the present invention, in the interleaver according to the 31st aspect, the characteristic correction means is a resistor which is energized to heat the optical waveguide.
In the 32nd aspect, the characteristic correction means is a resistor which is energized to generate heat to correct the characteristics of the optical waveguide.
In order to achieve the above object, according to the 33rd aspect of the present invention, three is provided an interleaver comprising an input waveguide and two optical waveguides which are connected to one end of the input waveguide and demultiplex input wavelength multiplexed light into light components of odd-numbered wavelengths and light components of even-numbered wavelengths, wherein at least one of the two optical waveguides is made of a material which changes a wavelength selection characteristic upon being heated or irradiated with ultraviolet light, and the characteristic of the optical waveguide is corrected by performing the heating or irradiation of ultraviolet light until a measurement result on an intensity of light emerging from the optical waveguide, which is obtained when light having a first wavelength xcex1 shifted from a specific wavelength by a predetermined wavelength is incident on the optical waveguide via the input waveguide, coincides with a measurement result on an intensity of light emerging from the optical waveguide, which is obtained when light having a second wavelength xcex2 symmetrical to the first wavelength xcex1 with respect to the specific wavelength is incident.
According to the 33rd aspect, at least one of the two optical waveguides connected to the input waveguide of the interleaver is made of a material which changes the wavelength selection characteristic upon heating or irradiation of ultraviolet light, and characteristics are corrected by measurement using the two wavelengths xcex1 and xcex2 having a predetermined relationship.
As obvious from the above aspects, according to the first aspect, second to fifth aspects, seventh aspect, eighth aspect, and 17th to 19th aspects, light having the first wavelength xcex1 shifted from the center wavelength xcexg as the correction target by the predetermined wavelength is incident on the waveguide component on the incident side. In this state, the level of output light is measured while the relative position of the two waveguide components is changed. In addition, light having the second wavelength xcex2 on the opposite side of the wavelength xcexg as a middle point to the first wavelength xcex1 is output, and similar measurement is performed. In the coincident position discrimination step, a relative movement position where the levels of the two light components coincide with each other is discriminated, and the positions of the two waveguide components in the direction crossing the optical axis are fixed to the discriminated relative movement position, thereby terminating correction of the center wavelength xcexg. This easily and quickly realizes correction.
According to the second aspect, sixth aspect, 20th aspect, or 26th aspect, since the first and second wavelengths xcex1 and xcex2 are time-divisionally measured, it suffices to move the relative position of the two waveguide components once. This makes it possible to realize quicker correction.
According to the fourth aspect or 22nd aspect, in the final correction step, measurement for obtaining a positional relationship is performed with respect to the light components respectively output from a plurality of output waveguides, and the positional relationship is fixed in accordance with the measurement results, thereby terminating correction of the center wavelength xcexg. This makes it possible to accurately correct the center wavelength xcexg in the overall optical element.
According to the fifth aspect or 23rd to 25th aspects, light having the first wavelength xcex1 shifted from the center wavelength xcexg as the correction target by the predetermined wavelength is incident on the waveguide component on the incident side. In this state, the level of output light is measured while the relative position of the two waveguide components is changed. In addition, light having the second wavelength xcex2 on the opposite side of the wavelength xcexg as a middle point to the first wavelength xcex1 is output, and similar measurement is performed. The coincident position discrimination means discriminates a relative movement position where the levels of the two light components coincide with each other, and the positions of the two waveguide components in the direction crossing the optical axis are fixed to the discriminated relative movement position, thereby terminating correction of the center wavelength xcexg. This easily and quickly realize correction.
According to the eighth aspect or 28th aspect, the final correction means performs measurement for obtaining a positional relationship with respect to the light components respectively output from a plurality of output waveguides, and the positional relationship is fixed in accordance with the measurement results, thereby terminating correction of the center wavelength xcexg. This makes it possible to accurately correct the center wavelength xcexg in the overall optical element.
According to ninth aspect or 12th aspect, the characteristics of a waveguide from which light having a predetermined wavelength is to be output can be easily and quickly corrected by using light components having two different wavelengths.
In addition, according to the 15th aspect or 16th aspect, whether a specific waveguide has a desired wavelength characteristic can be easily and quickly determined by using light components having two different wavelengths.
Furthermore, the arrayed waveguide diffraction grating according to the 29th aspect or 30th aspect includes a slab waveguide constituted by two waveguide components, various types of slab waveguides can be formed by properly selecting and using these waveguide components. In addition, a slab waveguide can be efficiently formed from one wafer. Since the characteristics of the arrayed waveguide diffraction grating are corrected by measurement using the two wavelengths xcex1 and xcex2 having a predetermined relationship, an improvement in productivity and a reduction in cost can be attained.
Moreover, according to the interleaver of the 31st to 33rd aspects, since the characteristics can be corrected by measurement using the two wavelengths xcex1 and xcex2 having a predetermined relationship, an improvement in productivity and a reduction in cost can be attained.
The above and many other objects, features and advantages of the present invention will become manifest to those skilled in the art upon making reference to the following detailed description and accompanying drawings in which preferred embodiments incorporating the principle of the present invention are shown by way of illustrative examples.